RESUMO
During the systematic investigation of the tin-rich side of the Tb-Sn binary system temperatures of non-variant transformations were established. The crystal structure of ßTb3Sn7 was determined for the first time from single-crystal diffraction data. Parameters of the unit cell have been determined previously by Manfrinetti & Palenzona [(1993), J. Alloys Compd. 201, 43-47], but the structure was not solved until now. The compound belongs to a new structure type with space group Pmmm. The unit cell contains two split positions: Sn7 (Wyckoff 1a), Sn7A (Wyckoff 2q) and Sn8 (Wyckoff 1d), Sn8A (Wyckoff 2s). Structures of both α- and ß-modifications of Tb3Sn7 can be described as close packing of the coordination polyhedra of Tb atoms. In turn these polyhedra can be constructed of fragments of simple AuCu3 and CsCl types.
RESUMO
A single crystal of penta-lanthanum dizinc stannide, La(5)Zn(2)Sn, was obtained from the elements in a resistance furnace. It belongs to the Mo(5)SiB(2) structure type, which is a ternary ordered variant of the Cr(5)B(3) structure type. The space is filled by bicapped tetra-gonal anti-prisms from lanthanum atoms around tin atoms sharing their vertices. Zinc atoms fill voids between these bicapped tetra-gonal anti-prisms. All four atoms in the asymmetric unit reside on special positions with the following site symmetries: La1 (..m); La2 (4/m..); Zn (m.2m); Sn (422).
